Welcome to the forum Shaun.
Lots of questions, but that's what the forum is for.
1/ Get yourself a Zodiac pressure gauge. The old alloy ones are great, but the new plastic ones will do. Takes the guess work out of tube pressures. I used to run a Zodiac MkII CGT, so similar to your Futura apart from speed tubes underneath. The main tubes were 240-280 millibar, and the inflatable keel was 220 millibar. The valves won't be inter-communicating which means you need to inflate sections individually and pressurise them evenly. The new Futura uses oversized tubes, so watch where you get information from, as pressures could be different. Yours looks like the conventional tube size.
2/ Rear cones will be part of main sponsons. Valve is normally located on tube. Should be at least 3 valves on 4.2m, not including speed tubes or keel.
3/ Not familiar with speed tubes, but given the size and diameter, it won't take much to pressurise them. If nozzle kicks back then its probably at pressure.
4/ Zodiacs have multi-chamber inflatable secions, so if one section fails, then the speed tubes, keel, and remaining inflated sections should provide buoyancy. One thing to watch - if internal baffle in tubes is damaged (over pressurising section) then the whole thing could deflate if section is damaged. Inflate the boat at all valves evenly. Try pressing valve (releases pressure) and see if whole section deflates? Only that particular section should deflate.
Regards patches. If in any doubt, renew them. You can inflate boat to pressure and try soapy water to reveal leaks. If patching, take your time and use 2-part Polymarine glue for PVC. Preparation is everything including ambient temperature, degreasing, etc. Details on Polymarine site.
5/ Year of manufacture is on Zodiac plate. Normally located on outside transom. The year of manufacture is normally last two digits after model ID.
6/ Lots of companies to choose from. Given you have new engine (and that's the desirable bit for thieves) then get a decent outboard lock on it, take a note of serial number and take plenty pictures. Craftinsure is who I use and are great, based on launch and retrieve, stored in garage, etc. Would expect to pay £100 or so for cover.
7/ Its a semi-recessed valve. The rubber diaphragms, valve and cap gaskets deteriorate over time. Replacements here: Zodiac and Bombard RIB Dinghy Inflatable Boat Valves
8/ Should be 220 millibar. Don't over-pressurise. The inflatable keel normally fails at bonded section near transom with wear and tear. Can be glued.
9/ No, always remove and replace. Use hair dryer or heat gun (carefully) to soften old glue to prize off old patch. Clean of old glue thoroughly, sand area, degrease etc. Full instructions here. http://www.polymarine.com/pdfs/RepairingTubesPVC.pdf
Good luck with the repairs.